Leaching and Sorption of Nitrogen and Phosphorus by Crop Residue

Overland flow from cropland areas often contains nutrients and residue materials can either contribute to runoff nutrient load through leaching or remove nutrients by sorption. Measurements were made of leaching and sorption of nitrogen and phosphorus from corn (Zea mays L.), soybean (Glycine max (L.) Merr.) and winter wheat (Triticum aestivum L. cv. Pastiche) residues placed in solutions containing inorganic nutrients. Variables used were type of residue material, nutrient constituent, solution concentration, and residue / solution contact time. For a given residue material and nutrient constituent, four different solution concentrations were used (PO4 -P: 0 to 16 g mL-1; NO3 -N and NH4 -N: 0 to 24 g mL-1), and changes in solution concentration over five selected residue / solution contact times (25 to 86400 sec) were measured. Soybean and wheat residue contained relatively small amounts of NO3 -N and therefore had minimal impact on the NO3 -N content of the solutions. An increase in initial solution concentration did not substantially affect PO4 -P leaching from corn and soybean residue but caused the amount of NH4 -N removed to decrease. As residue solution / contact time increased from 25 to 86400 s (1 day), the amount of PO4 -P leached from corn and soybean residue consistently increased. Wheat residue sorbed PO4 -P with an increase in sorption generally resulting from greater residue solution / contact time. Thus, crop residue materials appear to have the potential to influence the N and P content of runoff through leaching and sorption.